ارزيابي رفتار باربري پي‌هاي نواري بر روي خاك لايه ‌يي مسلح با ژيوگريد

Evaluation of Strip Footing Behavior Resting on Geogrid-Reinforced Soils

در شرايطي كه خاك زير پي ضعيف باشد و تحمل بارهاي وارده را نداشته باشد، بهسازي خاك با جايگزيني خاك مناسب، راهي منطقي و مناسب است. استفاده از مسلح كننده هاي ژيوگريد با توجه به مكانيزم اندركنش با خاك، امكان دستيابي به ظرفيت باربري بيشتر و يا كاهش ضخامت لايه‌ي متراكم را ممكن مي سازد. در اين نوشتار، ضمن بررسي اثر لايه‌ي جايگزين‌شده‌ي خاك دانه ‌يي سُست با خاك دانه ‌يي متراكم در ظرفيت باربري و نشست نهايي شالوده‌ي نواري به بررسي و تحليل اثر وجود مسلح كننده‌ي ژيوگريد در مرز دو لايه‌ي مذكور در محيط نرم افزار تفاضل محدودFLAC 2D پرداخته شده است. نتايج تحليل ها نشان مي دهند كه افزايش عمق لايه‌ي خاك متراكم بيشتر از 5/2 برابر عرض پي، تاثيري در افزايش ظرفيت باربري نهايي پي نواري نخواهد داشت و بهينه ترين بهسازي براي خاك سُست با شيوه‌ي جايگزيني لايه‌ي خاك متراكم، استفاده از مسلح كننده‌ي ژيوگريد با عرض كافي در مرز دو لايه و عمق بهسازي حدود 75/0 عرض پي است. همچنين اثر مسلح سازي خاك لايه ‌يي با افزايش عمق بهسازي كاهش مي يابد. استفاده از لايه‌ي مسلح كننده با عرض كمتر از 5 برابر عرض پي نيز پيشنهاد نمي شود.

When soil beneath a foundation is weak and cannot bear applied loads, an appropriate method of soil improvement is essential. In cases where weak soil is improved by a replacing method, the improvement depth, due to the stress distribution pattern, is of great importance. However, in some cases, it is very difficult or too expensive to provide enough improvement depth. Hence, additional bearing capacity or other improvement methods are required. Using a geogrid to reinforce soil is an effective alternative way to improve the bearing capacity more effectively and economically. In this paper, the effect of replacing a loose layer by a dense one on the bearing capacity and settlement of a strip footing has initially been investigated. Then, the influence of a geogrid layer placed on the interface of loose and dense layers is analyzed and investigated using finite difference FLAC ?D software. The numerical model is verified and calibrated using experimental data from a physical model developed in the Soil Laboratory of Amirkabir University. Analyses results show that increasing the depth of compacted soil layer by more than ??? times the width of the foundation, does not have a considerable effect on the ultimate bearing capacity of strip footings, and only settlements will decrease. Using a geogrid layer between loose and compacted soil will improve the bearing capacity greatly, for a modified depth less than ??? times the width of the foundation, The most efficient improvement in this method is when the geogrid layer is placed on the boundary of loose and dense layers at a depth of ???? the foundation width. The efficiency of reinforcement is reduced by increasing the improvement depth. Using a reinforced layer with a width of less than ??times the foundation width is not recommended.